1. Field
Methods and apparatuses consistent with exemplary embodiments disclosed herein relate to transmissive optical shutters and methods of fabricating the same.
2. Description of the Related Art
Recently, interest with respect to a three-dimensional (3D) camera module that provides a 3D image has increased. In particular, the demand for 3D content has increased, along with the development of a 3D display apparatus that displays a realistic 3-D image. Accordingly, many studies have been conducted about various apparatuses for obtaining a 3D image, by which a user may directly manufacture 3D content.
Depth information with respect to a distance between surfaces of an object and a 3D image pickup apparatus may be obtained by using a time-of-flight (TOF) method. The TOF method is a method of measuring an optical flight time of light that is irradiated from a laser beam to an object and is received by a light receiving unit after being reflected by the object. According to the TOF method, light having a specific wavelength (for example, infrared light having a wavelength of 850 nm or more) is irradiated to an object by using a light-emitting diode (LED) or a laser diode (LD). After receiving the light (reflected light) having the same wavelength reflected from the object, distance information is extracted. For example, after modulating an amplitude of the reflected light by using an optical shutter, a phase delay may be measured by capturing an image using an image pickup device, such as a charge coupled device (CCD) or a complementary metal-oxide semiconductor (CMOS) device. That is, a brightness image is obtained by accumulating or sampling the amount of light inputted to the image pickup device, and a phase delay and a distance may be calculated from the brightness image. According to the modulation method, in order to obtain an accurate phase delay, an optical shutter that may modulate light at a high speed of a few tens of MHz to a few hundreds of MHz is needed.
Recently, an optical shutter based on a gallium arsenide (GaAs) semiconductor that is easily realized, and may be operated at a low voltage but at very high speed while being small in size, has been proposed. The optical shutter based on the GaAs semiconductor has a structure in which a multiple quantum well (MQW) is disposed between a p type-electrode and an n-type electrode, and uses a phenomenon of absorbing light in the MQW when a reverse direction bias voltage is applied to both the p type-electrode and the n-type electrode. The optical shutters based on the GaAs semiconductor may be divided into two types including a reflective optical shutter and a transmissive optical shutter. In particular, when the transmissive optical shutter is used, the configuration of an optical system of a 3D image pickup apparatus is simple, and thus, the use of the transmissive optical shutter in the 3D image pickup apparatus may facilitate the miniaturization of the 3D image pickup apparatus.
In the optical shutter based on the GaAs semiconductor, a current should be rapidly and uniformly supplied from a p-type electrode disposed on a side of the optical shutter on which reflected light is incident, to a p-type GaAs layer formed below the p-type electrode.